Apparatus for drilling mutually intersecting parallel holes



Oct 23, 1962 N. A. HAGSTRC5M ETAL 3,059,977

APPARATUS FOR DRILLING MUTUALLY INTERSECTING PARALLEL HOLES Filed Sept. 28, 1959 2 Sheets-Sheet l 1962 N. AVHAGSTROM ETAL 3,059,977

APPARATUS FOR DRILLING MUTUAL-LY INTERSECTING PARALLEL HOLES Filed Sept. 28, 1959 2 Sheets-Sheet 2 United States Patent Oilice 3 ,059,977 Patented Oct. 23, 1962 3,059,977 APPARATUS FOR DRILLING MUTUALLY INTERSECTING PARALLEL HOLES Nils August Hagstriim and Bengt Paul Bjiirnson, Sandviken, Sweden, assignors to Sandviken Jernverks Aktiebolag, Sandviken, Sweden, a corporation of Sweden Filed Sept. 28, 1959, Ser. No. 842,799 Claims priority, application Sweden Oct. 3, 1958 7 Claims. (Cl. 308-4) This invention relates to an improved method of and apparatus for drilling at least two mutually intersecting, parallel holes, into rock for use in conjunction with rock blasting.

A known technique for the blasting of rock is to drill a plurality of holes into the face of the rock, these holes being arranged in accordance with a desired pattern that will establish the desired blast pattern. Various patterns for the drill holes or cuts are known and most of them feature a central hole of compartively large area surrounded by a plurality of holes of lesser area. The outer, small area holes only are loaded with explosive so that when the blasting actually occurs, movements of the rock toward the center can take place with a most favorable shattering effect. The larger, central hole can be cylindrical but it has been proved that a non-cylindrical central hole decreases the resistance of the rock to shattering. One known and advantageous configuration for such a non-cylindrical hole is that established by two or more mutually intersecting cylindrical holes having substan tially parallel axes. A hole of such configuration surrounded by twelve smaller holes in which the blasting charges are placed is known as a Coromant-cut.

A practical difliculty arises, however, in drilling the non-cylindrical central hole consisting of the two or more mutually intersecting cylindrical holes since it has been found to be quite difficult to produce these holes with their axes mutually parallel throughout their length which may run anywhere from 1.5 to meters. If the axes of the holes are not maintained mutually parallel, a satisfactory blast action of the cut will not be obtained.

The purpose of this invention is to provide an improved method of and apparatus for drilling the non-cylindrical hole and is distinguished principally by the features that one of two or more cylindrical holes is first drilled in the usual manner into the face of the rock to the required depth; a guide tube is then inserted into this hole, such tube being provided on its periphery with at least one groove extending longitudinally of the tube and parallel with the tube axis; and a second cylindrical hole is then drilled into the face of the rock, the drill bit being guided by the groove so that the second hole is formed parallel to the first and intersects the latter.

If the non-cylindrical configuration of the central hole is to be established by more than two intersecting cylindrical holes, the guide tube may be provided with a plurality of guide grooves arranged about its periphery and the one or more guide grooves may have different configurations, i.e., they may form part of a circular cylinder, or be parabolic or cornered, etc. If the groove is of circular configuration, its radius of curvature may be less than that of a circular tube in which it is located.

Preferably the invention also provides means for anchoring the guide tube in the first drilled hole by wedging an inner end portion of the tube radially outward against the wall of the drilled hole so as to prevent the guide tube from moving while the second hole is being drilled.

The invention is described in further detail in the following description and the accompanying drawings which illustrate the same. In these drawings:

FIG. 1 is a view in side elevation of one embodiment of a guide tube shown in its guiding relation to a drill bit in the act of drilling the second hole, the guide tube being already inserted in the first drilled hole;

FIG. 2 is a view in transverse section through the guide tube and showing also the tube in place in the first drilled cylindrical hole and the second drilled hole established by guiding the drilling bit along a groove in the guide tube;

FIG. 3 is a fragmentary view of a face portion of a rock wall which is to be blasted and with a pattern of holes drilled therein according to the so-called Coromant-cut;

FIG. 4 shows a part of the guide tube expander structure by which the guide tube is anchored in the first drilled hole so as to prevent any movment thereof while the second hole is being drilled;

FIG. 5 is a view in transverse section taken on line 5-5 of FIG. 6 and illustrating a modified embodiment of a guide tube and which is provided with a single guide groove as distinguished from the multiplicity of guide grooves provided on the guide tube shown in the embodiment of FIGS. 1 and 2;

FIG. 6 is a fragmentary longitudinal view in elevation of the modified, single grooved guide tube; and

FIG. 7 is a view in perspective showing a fragmentary longitudinal portion of the single-grooved guide tube.

With reference now to the drawings and to FIGS. 1 and 2 in particular, the periphery of the guide tube 11 is seen to be provided with a plurality of grooves 12 which extend longitudinally of the tube and parallel to the longitudinal axis. In this particular embodiment, there are six of the grooves 12 spaced uniformly about the periphery of the tube and they have a concave configuration. Those portions 12a of the wave form periphery of the tube between the grooves 12 are seen to be rounded convexly. The inner peripheral surface of the tube has the same configuration as the outer peripheral surface. Consequently, the tube is of uniform thickness throughout its length. The number of longitudinally extending grooves in the outer peripheral surface of the tube may be varied between one or two up to six or more. Actually, if the large central hole in the drilling face of the rock is to be composed of only two mutually intersecting cylindrical holes, the guide tube need be provided with only one guide groove for the cutting bit when cutting the second, intersecting hole.

In the illustrated, six-groove guide tube, a suitable outer diameter for the guide tube has been found to be between and mm., and preferably between 48 and 51 mm. The inner diameter can then be between 30 and 35 mm., and preferably about 3.3203 mm. The thickness of the tube wall can then be between 2 and 3 mm. The thickness of the tube wall is thus about from 4% to 6% of the outer diameter of the tube in order to establish sufiicient elasticity in the tube simulaneously with the necessary space to accommodate and permit operation of an expander element which will be later described and which is used to anchor or chuck the inner end portion of the guide tube in the first drilled hole.

The length of the guide tube 11 may be varied as the occasion requires and need be only long enough to properly guide the drilling bit parallel to the axis of the first drilled hole 17 when drilling the second and intersecting hole 23. Thus the guide tube 11 may extend along the entire length of the first drilled hole 17 or along only a part of the same. In the illustrated embodiment, FIG. 1, the guide tube extends for the full length of the first drilled hole 17, which length may vary from 1.5 to 5 meters, preferably about 3 meters. The guide tube may consist of a single structural unit, or it may be composed of two or more axial sections joined in end-to-end-rela-. tion.

As shown in FIG. 1, the left end of guide tube 11 is slotted longitudinally at 18 at every other ridge portion 12a for a certain length, for example from 10 to 20 mm. and the three portions of the tube between these slots are adapted to be engaged respectively by three tapered fins 19 of a draw rod 20 shown in FIG. 4 which extends longitudinally through the guide tube so as to force these tube portions resiliently outwardly against the wall at the bottom of the first drilled hole 17 and hence anchor or chuck the tube immovably in place as the draw rod is pulled to the right as seen in FIG. 1. The necessary axial displacement of draw rod 20 to cause the fins 19 to wedge the ridge portions 12a outwardly against the wall of the hole may be effected by means of a screw device 21 at the right end of rod 20 as seen in FIG. 1. To release the ridge portions 12a from the wall of the drill hole it is necessary only to loosen the screw device 21 so as to enable the draw rod 20 to be shifted in the opposite direction thus moving the fins 19 away from the ridge portions 12a and permitting the latter to move back toward the axis of the tube because of their inherent resiliency characteristic.

FIG. 3 illustrates a drill pattern in the face of the rock which is of the so-called Coromant-cut. This pattern is seen to be comprised of a centrally located, large, noncylindrical hole composed of two parallel extending and mutually intersecting, i.e. overlapping, holes 13, 14 which may be of the same or different diameters. In FIG. 3, these two center holes are illustrated as being of slightly different diameter. Around the composite, large central hole 13-14 are drilled a plurality of smaller cylindrical holes consisting of an inner set of six smaller holes 15 and an outer set of six other smaller cylindrical holes 16 located more remotely from the center hole 1314 than are the holes 15 of the inner set. In the illustrated embodiment, the holes 16 of the outer set are positioned in a symmetrical pattern with respect to the central large hole 13--14 and the holes 15 of the inner set are positioned somewhat unsymmetrically with respect to the inner hole 1314 in order to obtain a more effective blasting out of the cut. Explosive charges are placed in the holes 15, 16 but not in the central hole 13, 14.

As previously explained, it is essential that the two or more intersecting, central, cylindrical holes, which thereby jointly develop a larger non-cylindrical or slotlike hole, be drilled with their longitudinal axes mutually parallel. This is accomplished in the following manner:

One of the two intersecting holes to be formed is first drilled in a known manner with a drill bit such as the percussion drill bit 22 shown in FIG. 1 with, for example, four cutter inserts, arranged in x or cross form and which may or may not include grooves for removing drilled material. The first drilled hole is shown at 17 in FIG. 2 and corresponds generally to one of the two holes 13, 14 in FIG. 3. For a guide tube 11 of the dimensions previously given, the hole 17 could have a diameter of from 55-60 mm. so as to make it relatively easy for the guide tube 11 to be freely inserted in the hole, the slotted end 18 of the tube being inserted first. Draw rod 20 which is inserted ahead of the tube by a distance of about mm. is then pulled to the right so as to chuck or anchor the tube conventionally in the hole against any possible movement. Orientation of tube 11 in the first drilled hole 17 corresponding, for example, to hole 13 in FIG. 3, can be such that the particular groove 12 which is to be used for guiding of the drill bit in drilling the second hole 23, corresponding for example to hole 14 in FIG. 3, will be positioned directly above or below the center or axis of the tube. The advantage of this is that it thereby avoids any tendency to distort the desired direction of the second drill hole on account of the influence of gravity. The drill bit for the second hole, and possibly other holes in addition thereto, preferably has a smooth outer periphery and is devoid of grooves for drilled material in order to avoid damage to both bit and guide tube. However, other types of bits may be used.

The second hole 23 is now drilled and the drilling bit is guided by rotation in close contact with the guide groove 12. Consequently, as the drilling of the second hole 23 continues, the axis thereof will be maintained parallel to the axis of the first drilled hole 17 as the drill bit and the drill. rod attached thereto follow along the guide groove 12 longitudinally of tube 11.

If it is desired to drill other holes similar to the second hole 23 and which also intersect the first drilled hole 17, the guide tube 11 may be left in its chucked position in the hole 17 and the drilling of such other holes may then proceed in the same manner as used for drilling hole 23, using one or more of the other five guide grooves 12 provided in the guide tube. For example, the larger central hole can be made elongated in cross-section by drilling such an additional hole directly above the hole 23 and using the topmost guide groove 12 as viewed in FIG. 2 to guide the drill bit.

Moreover, the one or more additionally drilled holes which intersect with the first drilled hole 17 may have the same or different diameters. Also, with a guide tube such as shown in FIG. 2, and which is provided with a plurality of guide grooves 12, the useful life is extended since when one groove has been worn out, another can be presented for guiding the drill bit until it also has worn out.

The guide tube 24 in accordance with the modified construction shown in FIGS. 5-7 differs from that shown in FIGS. 1 and 2 only in that it is provided with but a single groove 25 extending longitudinally of the tube. Thus the periphery of tube 24 is cylindrical except for the concavely curved groove 25 which may form part of a circular cylinder, and which may have a radius of curvature less than that of the remainder of the periphery of the tube. As with the other tube which has been described, one end of tube 24 may be provided with longitudinal slots and an associated chucking or wedging device so as to enable the tube to be fastened securely in place within the first drilled hole. Drilling of the second hole with a guide tube of the construction shown in FIGS. 57 is accomplished in the same manner as has already been explained in connection with the embodiment of FIGS. 1 and 2. However, it should be noted that if additional holes intersecting with the first drilled holes are desired at other orientations about the first drilled hole, it will be necessary to unchuck the guide tube after each hole is drilled and rotate the same until the guide groove 25 reaches the new position for guiding the drill bit once again.

In conclusion, it is desired to point out that the inventive concept is not limited to the specific constructions which have been illustrated but may be departed from in various respects without, however, departing from the spirit and scope of the invention as defined in the appended claims. The improved method of and apparatus for drilling two parallel extending, mutually intersecting cylindrical holes which has been described makes it possible for a relatively unskilled driller to obtain the desired non-cylindrical big or center hole in a drill cut which can also serve as a guide hole for receiving a drill jig, the latter then being used as a guide also for drilling of the various other holes about the big hole, for example the holes 15 and 16 in the pattern according to FIG. 3.

We claim:

1. Apparatus for drilling a large area non-cylindrical hole into a rock face or the like, said non-cylindrical hole comprising at least two mutually intersecting cylindrical holes of smaller area having substantially parallel axes comprising a flexible, metal guide tube adapted to be inserted into a first drilled one of said cylindrical holes, said guide tube having a wall thickness of 23 mm. and being provided on its periphery with at least one groove extending longitudinally of the tube and parallel with the tube axis for guiding a drilling bit along said groove to drill the second cylindrical hole and said groove having a depth greater than the thickness of the tube wall.

2. Apparatus for drilling a non-cylindrical hole into a rock face as defined in claim 1 wherein said guide tube is provided with a plurality of said grooves arranged around the periphery thereof.

3. Apparatus for drilling a non-cyiindrical hole into a rock face as defined in claim 1 wherein said guide tube is provided with an even number of said grooves arranged uniformly about the periphery thereof.

4. Apparatus for drilling a non-cylindrical hole into a rock face as defined in claim 1 wherein said groove is arcuate in cross-section and the center of curvature of said concave groove lies outside of the periphery of said guide tube.

5. Apparatus for drilling a non-cylindrical hole into a rock face as defined in claim 1 wherein said guide tube is provided with a plurality of said grooves arranged around the periphery thereof, the bottom portions of said grooves being of concave curvature and the peripheral portions of said guide tube between said grooves being of convex curvature.

6. Apparatus for drilling a non-cylindrical hole into a rock face as defined in claim 1 and which further includes an expander device located within and coperative with one end portion of said tube for expanding the tube Wail outwardly against the surrounding wall of said first cylindrical hole.

7. Apparatus for drilling a non-cylindrical hole into a rock face as defined in claim 6 wherein one end portion of said tube is slotted longitudinally and said expander device includes tapered fins engageable with the portions of the tube periphery between said slots upon longitudinal displacement of said expander device within said tube for forcing said tube peripheral portions outwardly.

References Cited in the file of this patent UNITED STATES PATENTS 647,133 Emery Apr. 10, 1900 1,264,424 Mowlds Apr. 30, 1918 FOREIGN PATENTS 10,981 Great Britain June 27, 1891 512,478 Canada May 3, 1955 

